Early Calcium Monocarboaluminate Hydrate Formation in Cement Paste: Effect of Polycarboxylate Type Admixture

Effects of polycarboxylate type admixture (PCA) on calcium monocarboaluminate hydrate (AFmc) formation in hydrated cement paste containing limestone filler (LF) are investigated by the Fourier transform infrared spectroscopy (FTIR), the scanning electron microscopy (SEM), the derivative thermogravimetric (DTG) analysis and the adsorption amount measurement. Experimental results indicate that AFmc forms during the initial hydration period of cement as early as 15 min. It is found that PCA accelerates the early age AFmc formation and enhances cement hydration by promoting C4AF hydration at the early age, and, as a consequence, the iron associated AFmc phase forms more readily. The phenomenon is not observed when PCA is replaced by a naphthalene formaldehyde sulphonate condensate water reducer. Compatibility between PCA and cement is modified due to the presence of AFmc along with ettringite (AFt), which results in a less adsorption amount of PCA on the surface of cement minerals. As a kind of high-range water reducer, PCA may be the preferred choice for concrete containing LF.